SPONTANEOUS rupture of the internal mammary or epigastric vessels within the rectus muscle is a definite surgical entity, though rarely occurring, and hence lacking the familiarity characteristic of the average abdominal lesion. Examples of this condition are appended:CASE REPORTS Case i.-Male, age 55, had been driving an automobile over smooth roads for about four hours, after which time he turned the wheel over to his wife and settled back in the seat to rest his eyes and take a nap. Without any accountable reason, he suddenly became conscious of a mild, but sharply acute pain in the left side of his abdomen. This pain, at the end of 30 minutes, had increased to one of marked severity and the patient, being a doctor, feared that he had suffered an intestinal rupture or possibly a mesenteric thrombosis. There was no great shock, but he became nauseated and vomited. Two hours elapsed from the onset of the symptoms before he reached his home and received medical attention. The attending physician made a tentative diagnosis of some acute intra-abdominal lesion. He was taken to the hospital immediately, and was seen by the author shortly after admission.Physical Examination disclosed a heavy-set, stout man, suffering with very acute abdominal pain, so severe that he could not tolerate the weight of the bed clothes on his abdominal wall. There was a mass in the region of the left rectus muscle at about the level of the umbilicus which was exquisitely tender on palpation, and appeared to be about the size of a grapefruit. The left rectus muscle was tensely rigid above and below the mass, but the rigidity seemed to stop with a clear-cut line of demarcation along the midline of the abdomen, and the right rectus and right half of the abdomen were neither tender nor rigid. The left side of the abdomen showed some tenderness and rigidity spreading out into the oblique and transversalis group of muscles, but these phenomena tapered off completely-before reaching the anterior superior spine of the ilium. Temperature, IOO.60 F.; pulse, I20; blood pressure, 175/95. R.B.C., 4,500,000, hemoglobin, go per cent; W.B.C., I4,000, polys., 82 per cent. The bleeding and coagulation time were normal, and there was no reduction from the normal in the platelets.The abdomen was not distended. Nausea and vomiting had ceased; there was no mass to be felt by rectum, and the urine was negative for red blood cells and pus. Careful consideration was given to the possible diagnosis of incarcerated hernia, volvulus, mesenteric thrombosis or a ruptured viscus. Roentgenologic examination, made in both the supine and prone positions, revealed no evidence of subcutaneous emphysema or free air in the peritoneal cavity. Diagnosis: Spontaneous hemorrhage in the left rectus muscle.Operation.